Ah, that's better.
I was surprised.
I was surprised.
Appliance fuses
- Thread starter Ray Tay
- Start date
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Fuse values, cable sizes and current loading of the connected appliance. Could go on for literally years arguing if regulations are to be followed to the letter. Stuff the regs. Go back to the good old days and the use of common *******g sense.
It would appear that some kettle manufacturers have done just this. My company recently purchased a new kettle, 2200W fitted with 0.75mm cable, about 1m of it. The kettle takes around two minutes to boil a litre of water, and then shuts off automatically. If it is assumed that for two minutes in every 10 the connecting cable is experiencing an overload of a little over 50%, then it will have ample time to recover. If it should start to get "a bit warm" then it resistance will increase, causing V²/R losses. Should this become excessive (that is the cable starts to melt - unlikely unless some fidiot jammed the switch)) then the fuse will rupture, to make it fail-safe. Thus, I was able to issue a Pass on a PAT. (note that fidiot is not a typo!
)
It would appear that some kettle manufacturers have done just this. My company recently purchased a new kettle, 2200W fitted with 0.75mm cable, about 1m of it. The kettle takes around two minutes to boil a litre of water, and then shuts off automatically. If it is assumed that for two minutes in every 10 the connecting cable is experiencing an overload of a little over 50%, then it will have ample time to recover. If it should start to get "a bit warm" then it resistance will increase, causing V²/R losses. Should this become excessive (that is the cable starts to melt - unlikely unless some fidiot jammed the switch)) then the fuse will rupture, to make it fail-safe. Thus, I was able to issue a Pass on a PAT. (note that fidiot is not a typo!
)
Yes, there have been a few threads regarding seemingly undersized manufacturer's supplied cable.
The time factor is often omitted.
Suffice to say it is allowed and correct.
A bit like the DNOs. They can stuff more current down cables than we can.
The time factor is often omitted.
Suffice to say it is allowed and correct.
A bit like the DNOs. They can stuff more current down cables than we can.
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Yup they did! They didn't the first time in that section, but it definitely says plug top fuse. Don't tell BAS
When I used to fit handryers they nearly aways stated use a 10 amp fuse, though hardy anyone read the instructions, let alone change the 13 amp fuse in the Fcu
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I think there is generally a misunderstanding as to why we use a fuse and how it changes according to types of appliance.
The fuse in the plug is a special case. And it has changed over the years. Years ago before we joined the EU if may have been permissible for manufacturers to rely on the fuse in the plug. But on joining the EU it was agreed that since many countries did not have fused plugs if the appliance needs a fuse under 16A then it must be included in the appliance and they should not rely on the one in the plug as in other countries there may not be a fuse in the plug. There is some slight variation some countries do have both 6A and 16A sockets, if fact at one time we had 5 and 15 amp sockets. So when fitting a British plug it may be required to have a 3A fuse (equivalent to using a 6A socket) or a 13A fuse. These are considered as preferred sizes.
Although the same physical size of fuse fits a fused connection unit (FCU) the rules change. With a fixed appliance i.e. one which is not plugged in, the manufacturer can stipulate the fuse size, so with a FCU you have 1, 2, 3, 5, 7, 10 and 13 amp fuses and the manufacturer can say what size should be fitted. He can also stipulate the type and I have needed to fit semi-conductor fuses to protect some items. Depending on the type and shape and location of an appliance it may be that fitting the fuse inside would cause problems. So often in the instructions it will say how it is to be supplied and the commissioning engineer has to insure the requirements are complied with. Be is special breakers or special fuses be it motor rated or semi-conductor.
So open up your TV and likely the fuse is built into the TV. But install a three phase compressor and likely the fuses are in a box on a near by wall.
With the fuse in the plug it is often hard to tell what size would be required. Some times you get a label 3A fuse installed but often nothing. So in the main as already said fuse is selected to match the cable used. Using a plug in energy meter it can be set to record the maximum power used. The results can be quite a surprise. My old fridge/freezer showed about 70W on run and stated 70W on the label however on start it showed 10A or to compare 2300 watt. And it states in the instructions never supply from an extension lead. However when replaced again run around 70W and the max showed as 120W which would be the size of the de-frost heater. Reason for the lower power peak is the use of an inverter drive.
Washing machine also has an inverter drive. However I wanted to run the washing machine from an inverter and 4 massive batteries and the boat engine and wood burning stove resulted in an abundant supply of hot water. Other than a special washing machine designed for boats seem to remember over £1500 we failed to find any washing machine with hot and cold fill. On enquiry we find something to do with energy labels plus if you heat items like egg they can be very hard to remove so they work better is washing is started with cold water then heated as the items are being washed. So only old washing machines had no water heater. All new washers have the heater built in. And when we hunted we could not find one under 2.2kW with an inverter motor which could be powered from a simulated sine wave.
So my dad taught me to read the appliance plate and if heating fit a fuse to just take that power, and if motor fit next size up. Which was the correct method in 1960 and still correct with a FCU. But with a plug look at size of cable under 1mm² fit a 3A otherwise fit a 13A. Nothing to do with perceived common sense, but more to do with being a member of the EU and all equipment should work in any member country simply by swapping the plug.
The fuse in the plug is a special case. And it has changed over the years. Years ago before we joined the EU if may have been permissible for manufacturers to rely on the fuse in the plug. But on joining the EU it was agreed that since many countries did not have fused plugs if the appliance needs a fuse under 16A then it must be included in the appliance and they should not rely on the one in the plug as in other countries there may not be a fuse in the plug. There is some slight variation some countries do have both 6A and 16A sockets, if fact at one time we had 5 and 15 amp sockets. So when fitting a British plug it may be required to have a 3A fuse (equivalent to using a 6A socket) or a 13A fuse. These are considered as preferred sizes.
Although the same physical size of fuse fits a fused connection unit (FCU) the rules change. With a fixed appliance i.e. one which is not plugged in, the manufacturer can stipulate the fuse size, so with a FCU you have 1, 2, 3, 5, 7, 10 and 13 amp fuses and the manufacturer can say what size should be fitted. He can also stipulate the type and I have needed to fit semi-conductor fuses to protect some items. Depending on the type and shape and location of an appliance it may be that fitting the fuse inside would cause problems. So often in the instructions it will say how it is to be supplied and the commissioning engineer has to insure the requirements are complied with. Be is special breakers or special fuses be it motor rated or semi-conductor.
So open up your TV and likely the fuse is built into the TV. But install a three phase compressor and likely the fuses are in a box on a near by wall.
With the fuse in the plug it is often hard to tell what size would be required. Some times you get a label 3A fuse installed but often nothing. So in the main as already said fuse is selected to match the cable used. Using a plug in energy meter it can be set to record the maximum power used. The results can be quite a surprise. My old fridge/freezer showed about 70W on run and stated 70W on the label however on start it showed 10A or to compare 2300 watt. And it states in the instructions never supply from an extension lead. However when replaced again run around 70W and the max showed as 120W which would be the size of the de-frost heater. Reason for the lower power peak is the use of an inverter drive.
Washing machine also has an inverter drive. However I wanted to run the washing machine from an inverter and 4 massive batteries and the boat engine and wood burning stove resulted in an abundant supply of hot water. Other than a special washing machine designed for boats seem to remember over £1500 we failed to find any washing machine with hot and cold fill. On enquiry we find something to do with energy labels plus if you heat items like egg they can be very hard to remove so they work better is washing is started with cold water then heated as the items are being washed. So only old washing machines had no water heater. All new washers have the heater built in. And when we hunted we could not find one under 2.2kW with an inverter motor which could be powered from a simulated sine wave.
So my dad taught me to read the appliance plate and if heating fit a fuse to just take that power, and if motor fit next size up. Which was the correct method in 1960 and still correct with a FCU. But with a plug look at size of cable under 1mm² fit a 3A otherwise fit a 13A. Nothing to do with perceived common sense, but more to do with being a member of the EU and all equipment should work in any member country simply by swapping the plug.
D
Deleted member 18243
To change the subject slightly: Where I work we have CNC machines on 3P supplies. Some are connected via MCBs in a distribution board, whilst others are connected to an overhead busbar, with cartridge fuses in the busbar plug. I've not got much experience with 3P, but one thing I distinctly remember from college is that on a 3 phase MCB the 3 breakers are physically connected, so that all phases will be disconnected if only one fails. With the busbar connector however, single fuses can (and do) blow, leaving the other 2 phases live.
What determines whether you must use a linked MCB or individual cartridge fuses?
K
kai
The safest solution would be an on-board MCB in the machine inlet itself - which would cut off all three phases in the event of a fault appearing on any one of the phases. That's the big advantage of MCB's over fuses in three phase work. I saw such a setup in my old workplace, a set of three BS88 fuses fed a Crabtree Model C50 breaker (20amps) and the isolator powering the mixing machine thereafter. The BS88's were only there for the short-circuit protection, whilts the C50 breaker was for phase failure protection.
A 3ph mcb is a multipole device so MUST have all poles make and break together, as per reg 530.3.1 whereas fuses are not
Afaik if the circuits designed right you can still use fuses as in your case, as well as in 3phase Bs88 boards and 3 phase switchfuses where theres always a chance of 2 phasing the loads.
Things nowadays would have internal protection from 2 phasing damage nowadays one would hope, mcbs or fuses would not be that much help if one phase of the supply to the premises fail
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Not always easy to prevent single phasing when a fuse blows, it does seem odd maths wise that three fuses supply three phase and two fuses supply single phase but with no neutral it is a single phase only if a neutral is used would it be two phase or split phase. Using 400 volt control will ensure if either of the two phases fail then the machine will shut down, but to include the third needs some form of relay. In the main loss of a phase will mean an overload so the overload protection will open. Machine design can help have the Estop system use a different pair of phases to the main control circuits for example.
The big advantage of the MCB is you can switch the neutral with fuses the neutral can't have a fuse because of not being able to link. With a three phase motor once the motor is turning losing a phase is often heard well before the motor trips as it generates the missing phase so although one would think that using of different phases for the two controls would ensure is a phase is lost the contactors and relays would open often this is not the case. So there is a market for devices like this
designed to detect a loss of a phase.
The big advantage of the MCB is you can switch the neutral with fuses the neutral can't have a fuse because of not being able to link. With a three phase motor once the motor is turning losing a phase is often heard well before the motor trips as it generates the missing phase so although one would think that using of different phases for the two controls would ensure is a phase is lost the contactors and relays would open often this is not the case. So there is a market for devices like this
We are.
This is how you work it out.
There are two factors over which you have little or no control.
- The size of the load - let's call the current it draws Ib
- The size of the flex - let's call the maximum current it can handle Iz
The requirement is Ib ≤ In ≤ Iz.
The fuse rating can be anywhere in the green zone:
There is no reason to strive to get it as close to Ib as possible.
The disconnection of all phases must occur if one fuse blows or one phase is lost due to a fault elsewhere in the supply network.
A "lost phase" detector can be used between the fuses and the load to operate ( or drop out if fail safe required ) a 3 phase contactor. Sometimes this is incorporated in the Start-Stop controls of the machine.
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